Marble Run

This weekend we've been playing a lot with my marble run. I really enjoy filling it completely with marbles.




Daddy and I also like to do a version of mythbusters with the marble run. The latest myths we've been studying involve these two "Y" sections of the marble run, where the marbles can either go to the left or to the right. The way the marble run is formed, there's a "Y" early in the run and a "Y" later in the run. The marble has to pass through both Y's to land in the red or green bins but only the first Y to land in the yellow bin. The myth is that the marble is equally likely to land in any of the three bins. We busted that myth--a marble is more likely to land in yellow than either of the other two bins. We also checked that the Y's are "fair" in that the marble is just as likely to go left as right. So, how do you solve this mystery?